Simultaneous Adsorption of Arsenate and Chromate by Goethite: Effect of Humic Acid, Kaolinite, and Calcite

This study designed laboratory-scale experiments to investigate the efficiency of the simultaneous adsorption of AsV and CrVI onto goethite nanorods (GN) and to evaluate the influence of humic acid (HA), calcite, and kaolinite, three selected geochemical components, on the adsorption efficiency and reaction mechanisms. The findings revealed that kaolinite, HA, and calcite were ineffective in adsorbing AsV from the solution. In contrast, GN exhibited a 66% adsorption efficiency for As. For CrVI, GN demonstrated the highest removal efficiency (90.8%), while HA showed the lowest performance (60%). The presence of CrVI in the solution did not significantly impact AsV adsorption by the adsorbents. However, HA, kaolinite, and calcite notably reduced the adsorption efficiency of GN toward AsV. Conversely, the adsorption of CrVI by all adsorbents was negatively influenced by the presence of AsV in the solution. X-ray photoelectron spectroscopy analysis supported the batch experiment results, confirming that no oxidation or reduction reactions occurred during the adsorption process, as the valence states of As and Cr remained unchanged from their initial states in the solution. The simultaneous adsorption of As and Cr by GN in mixed solutions, particularly in the presence of geochemical components, proved to be a complex process. Across all experiments, Cr adsorption was consistently hindered by the presence of As. These results provide valuable insights for designing remediation strategies for water contaminated with both chromate and arsenate. Tailoring the approach to the specific geochemical composition of the affected area can enhance the effectiveness of surface and groundwater remediation.